Method and apparatus for adjusting channel quality indicator feedback period to increase uplink capacity

ABSTRACT

A method and apparatus for adjusting a channel quality indicator (CQI) feedback period to increase uplink capacity in a wireless communication system are disclosed. The uplink capacity is increased by reducing the uplink interference caused by CQI transmissions. A wireless transmit/receive unit (WTRU) monitors a status of downlink transmissions to the WTRU and sets the CQI feedback period based on the status of the downlink transmissions to the WTRU. A base station monitors uplink and downlink transmission needs. The base station determines the CQI feedback period of at least one WTRU based on the uplink and downlink transmission needs and sends a command to the WTRU to change the CQI feedback period of the WTRU.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application No.60/710,986 filed Aug. 24, 2005, which is incorporated by reference as iffully set forth.

FIELD OF INVENTION

The present invention is related to a wireless communication system.More particularly, the present invention is related to a method andapparatus for adjusting a channel quality indicator (CQI) feedbackperiod to increase uplink capacity in a wireless communication system.

BACKGROUND

In a wireless communication system, such as universal mobiletelecommunication services (UMTS) terrestrial radio access (UTRA), awireless transmit/receive unit (WTRU) sends a channel quality indicator(CQI), (or channel quality estimates), to a base station. The CQI isused for adaptive modulation and coding (AMC), channel sensitivescheduling, or the like. The base station determines an optimalmodulation scheme and coding rate for the WTRUs based on the reportedCQIs. The base station also uses the reported CQIs when determiningwhich WTRUs should be allowed for transmission.

The frequency of generation and transmission of the CQIs is controlledby parameters specified by a radio network controller (RNC). Theparameters are given to the WTRU through radio resource control (RRC)signaling at call setup or upon reconfiguration.

The transmission of CQIs by the WTRUs, although beneficial foroptimizing the capacity on the downlink, generates interference on theuplink. This interference may decrease the uplink capacity of thewireless communication system when the number of WTRUs that are requiredto transmit a CQI is large. Furthermore, it is often the case that thetransmission of CQIs by certain WTRUs is superfluous. Such a situationarises when a WTRU has no pending transmission on the downlink due to aperiod of inactivity at the application level.

The interference caused by the transmission of CQIs from non-activeWTRUs may be reduced by updating the CQI parameters so that the CQIs aregenerated by those WTRUs less frequently. However, this approach doesnot work well in practice because the CQI parameter update is performedthrough the RRC signaling, which is slow. By the time the CQI parameterupdate is communicated to the WTRU, the user of the WTRU may haveresumed activity, and performance would suffer until a new update issent to restore the original frequency of CQI generation.

In addition, in some circumstances it is desirable to reduce theinterference from CQI transmissions during a limited period of time inorder to increase the capacity available on the uplink when there is atemporary need for more capacity, (e.g., when one user has a largeamount of data to upload, such as a picture).

Therefore, it is desirable to provide a method to adjust the CQIfeedback period more quickly and efficiently to increase uplinkcapacity.

SUMMARY

The present invention is related to a method and apparatus for adjustinga CQI feedback period to increase uplink capacity in a wirelesscommunication system. The uplink capacity is increased by reducing theuplink interference caused by CQI transmissions. In accordance with afirst embodiment of the present invention, a WTRU monitors a status ofdownlink transmissions to the WTRU and sets the CQI feedback periodbased on the status of the downlink transmissions to the WTRU. Inaccordance with a second embodiment of the present invention, a basestation monitors uplink and downlink transmission needs. The basestation determines the CQI feedback period of at least one WTRU based onthe uplink and downlink transmission needs and sends a command to theWTRU to change the CQI feedback period of the WTRU.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of a process for adjusting a CQI feedbackperiod in accordance with a first embodiment of the present invention.

FIG. 2 is a flow diagram of a process for adjusting a CQI feedbackperiod in accordance with a second embodiment of the present invention.

FIG. 3 is a block diagram of a WTRU which implements the process of FIG.1.

FIG. 4 is a block diagram of a base station which implements the processof FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

When referred to hereafter, the terminology “WTRU” includes but is notlimited to a user equipment, a mobile station (STA), a fixed or mobilesubscriber unit, a pager, or any other type of device capable ofoperating in a wireless environment. When referred to hereafter, theterminology “base station” includes but is not limited to a Node-B, asite controller, an access point (AP) or any other type of interfacingdevice in a wireless environment.

The features of the present invention may be incorporated into anintegrated circuit (IC) or be configured in a circuit comprising amultitude of interconnecting components.

FIG. 1 is a flow diagram of a process 100 for adjusting a CQI feedbackperiod in accordance with a first embodiment of the present invention.In accordance with the first embodiment, a WTRU autonomously adjusts theCQI feedback period based on downlink transmission status. The WTRU isinitially configured with a normal CQI feedback period, and the WTRUreports a CQI to a base station via an uplink channel every CQI feedbackperiod.

The WTRU monitors the status of downlink transmissions to the WTRU (step102). In monitoring the downlink transmission status, the WTRU maymaintain a counter for counting the number of consecutive transmissiontime intervals (TTIs) that do not include a transmission for the WTRU.For example, in high speed downlink packet access (HSDPA), the number ofTTIs that do not include a transmission for the WTRU may be determinedby detecting a valid cyclic redundancy check (CRC) on downlinktransmissions on a high speed shared control channel (HS-SCCH). Thecounter is reset when a valid downlink transmission to the WTRU isdetected, (e.g., in HSDPA, a valid CRC is detected on the HS-SCCH).

The WTRU then adjusts the CQI feedback period based on the status of thedownlink transmissions (step 104). A piece-wise function or a look-uptable (LUT) may be used to select a new CQI feedback period based on thecounter value, such that the CQI feedback period is increased as thecounter value increases, and the CQI feedback period is decreased as thecounter value decreases. An exemplary mapping scheme for mapping thecounter value to the CQI feedback period is shown in Table 1. As shownin Table 1, the increased CQI feedback periods may be a factor of thenormal CQI feedback period. The base station may monitor and detect CQIsfrom the WTRU every normal CQI feedback period regardless of the CQIfeedback period setting in the WTRU. With this scheme, it is avoidableto miss CQIs due to inconsistent CQI feedback period settings in theWTRU and the base station. The parameters in Table 1 are configurablevia a higher layer signaling, which is preferably performed at callsetup. TABLE 1 The number of TTIs without a transmission for the WTRUCQI feedback period  0-31 normal feedback period, P 32-63 2P  64-127 3P128-511 4P 512 or higher 5P

Alternatively, the WTRU may be given multiple CQI feedback periods, (forexample, two (2) CQI feedback periods: an active CQI feedback period andan inactive CQI feedback period), via RRC signaling, and may switchbetween the CQI feedback periods in accordance with the counter value,(i.e., the number of TTIs without a transmission for the WTRU). Forexample, when the counter value is below a threshold, the active CQIfeedback period is selected, and when the counter value is equal to orabove the threshold, the inactive CQI feedback period is selected.

After the WTRU adjusts the CQI feedback period based on the status ofthe downlink transmissions, the process 100 returns to step 102 tofurther monitor the downlink transmission status.

FIG. 2 is a flow diagram of a process 200 for adjusting a CQI feedbackperiod in accordance with a second embodiment of the present invention.In accordance with the second embodiment, a base station sends a commandto increase or decrease the CQI feedback period of the WTRUs based onuplink and downlink transmission needs. The base station increases theCQI feedback period, (which means less frequent CQI feedbacks), when theuplink transmission needs increase, while the downlink transmissionneeds can still be supported with the less frequent CQI feedbacks. Asfrequent CQI feedbacks are beneficial to downlink performance, the basestation trades downlink capacity for uplink capacity on a short termbasis.

The base station monitors uplink transmission needs and downlinktransmission needs (step 202). The uplink and downlink transmissionneeds are determined based on an amount of data buffered in each of theWTRUs for uplink transmissions and an amount of data buffered in a basestation for downlink transmissions to each of the WTRUs, respectively.The amount of data buffered in the WTRU for uplink transmission isindicated by the WTRU. For example, such indication may be given by ascheduling request, a happy bit or traffic volume measurement as in UTRARelease 6.

Alternatively, the base station may estimate the time required totransmit the data currently in the buffer of each WTRU and the timerequired to transmit the data buffered in the base station for each WTRUbased on average downlink and uplink throughput to and from each of theWTRUs.

The base station determines whether it is desirable to change the CQIfeedback period of at least one WTRU based on the uplink transmissionneeds and the downlink transmission needs (step 204). The base stationmay increase the CQI feedback period when the uplink transmission needsare high and the downlink transmission needs are low, and may decreasethe CQI feedback period, (or restore the original CQI feedback period),when the uplink transmission needs are low or the downlink transmissionneeds are high.

For example, if, for at least one WTRU, the estimated time required totransmit data in a buffer of the WTRU exceeds a pre-determinedthreshold, (i.e., the uplink transmission needs are high), it isdesirable to reduce the interference caused by CQI transmissions byincreasing the CQI feedback period. Therefore, the base stationdetermines if some or all of the downlink transmissions could affordless frequent CQI feedbacks. In order to determine this, the basestation may determine if the estimated time required to transmit thedata in the buffer of the base station on the downlink is within apre-determined threshold. If it is determined that some or all of thedownlink transmissions may afford less frequent CQI transmissions,(e.g., the estimated time required to transmit the data in the buffer ofthe base station is within the predetermined threshold), the basestation determines to increase the CQI feedback period.

If it is determined at step 204 that it is not desirable to change theCQI feedback period, the process returns to step 202 to further monitorthe uplink and downlink transmission needs. If it is determined at step204 that it is desirable to change the CQI feedback period, the basestation then sends a command to at least one WTRU to change the CQIfeedback period of the WTRU (step 206). After sending the command, theprocess 200 returns to step 202 to monitor the uplink and downlinktransmission needs.

If the base station subsequently determines that restoring the originalCQI feedback period is desirable for some or all of the WTRUs, (i.e., ifthe base station determines that the estimated time required to transmitthe data in the buffer of the base station on the downlink exceeds thepre-determined threshold, or if the base station determines that theestimated time required to transmit the data in the buffer of each ofthe WTRUs on the uplink is below the pre-determined threshold), the basestation sends a command to some or all WTRUs to restore the original CQIfeedback period of their CQI transmissions.

The command must be transmitted quickly, (e.g., within a few tens ofmilliseconds), to the concerned WTRUs or all WTRUs after a decision ismade by the base station. The command may be transmitted by any suitablemeans. For example, in UTRA Release 6, the command may be sent via anHS-SCCH. During each 2 ms TTI, the HS-SCCH includes informationnecessary for each WTRU to determine if any data will be transmitted tothe WTRU in the next TTI. The HS-SCCH includes bits for indicating achannelization code set combination for the WTRU. Currently, there areeight (8) unused bit combinations for the channelization code setcombinations. One of the 8 unused bit combinations may be used for thepurpose of sending the command to change the CQI feedback period. Forexample, one of the unused bit combinations may be used to signal anincrease of the CQI feedback period and another to signal a restorationof the original CQI feedback period.

The amount of change of the CQI feedback period in response to thecommand from the base station may be pre-determined, (e.g., by a factorof 2). Increase of the CQI feedback period by a factor of 2 means thatevery other CQI that would normally be transmitted with the originalconfiguration is now not transmitted. Alternatively, the amount ofchange of the CQI feedback period in response to the command may besignaled upon call setup or reconfiguration. For example, two sets ofCQI feedback periods may be given to the WTRU, and switched inaccordance with the command.

The information contained in a specific TTI in an HS-SCCH is normallyonly used by one specific WTRU, which is identified through bit-maskingof the CRC field with a WTRU-specific sequence, (WTRU identity (ID)). Inorder to provide a significant interference reduction on the uplinkwithin a short amount of time, it is desirable that all WTRUs monitoringa given HS-SCCH be commanded a change of the CQI feedback period at thesame time. Therefore, a special WTRU ID for all WTRUs may be used totransmit the command via the HS-SCCH.

FIG. 3 is a block diagram of a WTRU 300 which implements the process 100of FIG. 1. The WTRU 300 includes a downlink status monitor 302, a CQIfeedback controller 304 and an LUT 306 (optional). The downlink statusmonitor 302 monitors a status of downlink transmissions to the WTRU. Thedownlink status monitor 302 may include a counter 308 to count thenumber of consecutive TTIs that do not include transmissions to theWTRU. The CQI feedback controller 304 sets the CQI feedback period basedon the status of the downlink transmissions to the WTRU as statedhereinabove.

FIG. 4 is a block diagram of a base station 400 which implements theprocess 200 of FIG. 2. The base station 400 includes a monitor 402 and aCQI feedback controller 404. The monitor 402 monitors uplinktransmission needs and downlink transmission needs. The CQI feedbackcontroller 404 determines the CQI feedback period of at least one WTRUbased on the uplink transmission needs and the downlink transmissionneeds and sends a command to at least one of the WTRUs to change the CQIfeedback period.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

1. In a wireless communication system including a plurality of wirelesstransmit/receive units (WTRUs) and a base station wherein the WTRUsreport a channel quality indicator (CQI) to the base station every CQIfeedback period, a method for adjusting the CQI feedback period toincrease uplink capacity, the method comprising: a WTRU monitoring astatus of downlink transmissions to the WTRU; and the WTRU setting theCQI feedback period based on the status of the downlink transmissions tothe WTRU.
 2. The method of claim 1 wherein the status of downlinktransmissions is monitored by counting the number of consecutivetransmission time intervals (TTIs) that have no transmissions to theWTRU.
 3. The method of claim 2 wherein the CQI feedback period is setbased on the number of consecutive TTIs that have no transmissions tothe WTRU.
 4. The method of claim 1 wherein the CQI feedback period isset by using a look-up table (LUT) to map the status of downlinktransmission to one of a plurality of CQI feedback periods.
 5. Themethod of claim 4 wherein the LUT is configurable by a higher layersignaling.
 6. The method of claim 4 wherein the CQI feedback periods area factor of a normal CQI feedback period.
 7. The method of claim 6wherein the base station monitors CQI feedback from the WTRU everynormal CQI feedback period.
 8. The method of claim 3 wherein the CQIfeedback period is set by using a piece-wise function to map the statusof downlink transmission to one of a plurality of CQI feedback periods.9. The method of claim 3 wherein the WTRU is given an active CQIfeedback period and an inactive CQI feedback period, and the active CQIfeedback period is selected when the number of consecutive TTIs thathave no transmissions to the WTRU exceeds a threshold, otherwise theinactive CQI feedback period is selected.
 10. In a wirelesscommunication system including a plurality of wireless transmit/receiveunits (WTRUs) and a base station wherein the WTRUs report a channelquality indicator (CQI) to the base station every CQI feedback period, amethod for adjusting CQI feedback period to increase uplink capacity,the method comprising: a base station monitoring uplink and downlinktransmission needs; the base station determining whether it is desirableto change the CQI feedback period of at least one WTRU based on theuplink and downlink transmission needs; and if it is determined that itis desirable to change the CQI feedback period, the base station sendinga command to the WTRU to change the CQI feedback period of the WTRU. 11.The method of claim 10 wherein the base station sends the command toincrease the CQI feedback period of the WTRU when the uplinktransmission needs exceed a first threshold and the downlinktransmission needs are within a second threshold.
 12. The method ofclaim 10 wherein the base station sends the command to decrease the CQIfeedback period when either the uplink transmission needs are within thefirst threshold or the downlink transmission needs exceed the secondthreshold.
 13. The method of claim 10 wherein the uplink transmissionneeds are determined based on an amount of data buffered in each of theWTRUs for uplink transmissions and the downlink transmission needs aredetermined based on an amount of data buffered in the base station fordownlink transmissions to each of the WTRUs.
 14. The method of claim 10wherein the uplink transmission needs are determined based on a timerequired to transmit the data buffered in each of the WTRUs, and thedownlink transmission needs are determined based on a time required totransmit the data buffered in the base station for each of the WTRUs.15. The method of claim 13 wherein the amount of data buffered in theWTRU is reported by the WTRU.
 16. The method of claim 15 wherein theamount of data buffered in the WTRU is indicated by a scheduling requestsent by the WTRU.
 17. The method of claim 15 wherein the amount of databuffered in the WTRU is indicated by a happy bit sent by the WTRU. 18.The method of claim 15 wherein the amount of data buffered in the WTRUis indicated by traffic volume measurement.
 19. The method of claim 10wherein the base station broadcasts the command to all WTRUs.
 20. Themethod of claim 10 wherein the base station sends the command only toconcerned WTRUs.
 21. The method of claim 10 wherein the downlinktransmissions is transmitted via high speed downlink packet access(HSDPA).
 22. The method of claim 21 wherein the command is transmittedvia a high speed shared control channel (HS-SCCH).
 23. The method ofclaim 22 wherein the command is transmitted by using an unusedchannelization code set combinations.
 24. The method of claim 22 whereinthe command is transmitted using a special WTRU identity (ID) for allWTRUs.
 25. The method of claim 10 wherein an amount of change of the CQIfeedback period in response to the command is predetermined and signaledto the WTRUs, whereby the WTRU changes the CQI feedback period based onthe predetermined amount of change.
 26. The method of claim 10 wherein aplurality of CQI feedback periods are given to the WTRUs in advance andone of the CQI feedback periods is selected in accordance with thecommand.
 27. The method of claim 10 wherein the CQI feedback periods aredetermined as a factor of a normal CQI feedback period.
 28. The methodof claim 27 wherein the base station monitors CQI feedback from the WTRUevery normal CQI feedback period.
 29. In a wireless communication systemincluding a plurality of wireless transmit/receive units (WTRUs) and abase station wherein the WTRUs report a channel quality indicator (CQI)to the base station via an uplink channel every CQI feedback period, aWTRU for adjusting the CQI feedback period to increase uplink capacity,the WTRU comprising: a downlink status monitor for monitoring a statusof downlink transmissions to the WTRU; and a CQI feedback controller forsetting the CQI feedback period based on the status of the downlinktransmissions to the WTRU.
 30. The WTRU of claim 29 wherein the downlinkstatus monitor includes a counter to count the number of consecutivetransmission time intervals (TTIs) that have no transmissions to theWTRU, whereby the CQI feedback controller sets the CQI feedback periodbased on a counter value.
 31. The WTRU of claim 30 further comprises alook-up table (LUT) for mapping the counter value to one of a pluralityof CQI feedback periods, whereby the CQI feedback controller sets theCQI feedback period by using the LUT.
 32. The WTRU of claim 30 whereinthe LUT is configurable by a higher layer signaling.
 33. The WTRU ofclaim 30 wherein the CQI feedback periods are determined as a factor ofa normal CQI feedback period.
 34. The WTRU of claim 30 wherein the CQIfeedback controller sets the CQI feedback period by using a piece-wisefunction.
 35. The WTRU of claim 30 wherein the WTRU is given an activeCQI feedback period and an inactive CQI feedback period, and the CQIfeedback controller selects the active CQI feedback period when thenumber of consecutive TTIs that have no transmissions to the WTRUexceeds a threshold, otherwise selects the inactive CQI feedback period.36. In a wireless communication system including a plurality of wirelesstransmit/receive units (WTRUs) and a base station wherein the WTRUsreport a channel quality indicator (CQI) to the base station via anuplink channel every CQI feedback period, a base station for adjustingCQI feedback period to increase uplink capacity, the base stationcomprising: a monitor for monitoring uplink and downlink transmissionneeds; and a CQI feedback controller for determining whether it isdesirable to change the CQI feedback period of at least one WTRU basedon the uplink and downlink transmission needs and sending a command tothe WTRU to change the CQI feedback period of the WTRU.
 37. The basestation of claim 36 wherein the CQI feedback controller sends a commandto increase the CQI feedback period of the WTRU when the uplinktransmission needs exceed a first threshold and the downlinktransmission needs are within a second threshold.
 38. The base stationof claim 36 wherein the CQI feedback controller sends a command todecrease the CQI feedback period when either the uplink transmissionneeds are within the first threshold or the downlink transmission needsexceed the second threshold.
 39. The base station of claim 36 whereinthe monitor monitors the uplink transmission needs based on an amount ofdata buffered in each of the WTRUs for uplink transmissions and monitorsthe downlink transmission needs based on an amount of data buffered inthe base station for downlink transmissions to each of the WTRUs. 40.The base station of claim 36 wherein the monitor monitors the uplinktransmission needs based on a time required to transmit the databuffered in each of the WTRUs, and monitors the downlink transmissionneeds based on a time required to transmit the data buffered in the basestation for each of the WTRUs.
 41. The base station of claim 39 whereinthe amount of data buffered in the WTRU is reported by the WTRU.
 42. Thebase station of claim 41 wherein the amount of data buffered in the WTRUis indicated by a scheduling request sent by the WTRU.
 43. The basestation of claim 41 wherein the amount of data buffered in the WTRU isindicated by a happy bit sent by the WTRU.
 44. The base station of claim41 wherein the amount of data buffered in the WTRU is indicated bytraffic volume measurement.
 45. The base station of claim 36 wherein theCQI feedback controller broadcasts the command to all WTRUs.
 46. Thebase station of claim 36 wherein the CQI feedback controller sends thecommand only to concerned WTRUs.
 47. The base station of claim 36wherein the downlink transmissions is transmitted via high speeddownlink packet access (HSDPA).
 48. The base station of claim 47 whereinthe CQI feedback controller sends the command via a high speed sharedcontrol channel (HS-SCCH).
 49. The base station of claim 48 wherein theCQI feedback controller sends the command using an unused channelizationcode set combinations.
 50. The base station of claim 48 wherein the CQIfeedback controller sends the command using a special WTRU identity (ID)for all WTRUs.
 51. The base station of claim 36 wherein the monitormonitors CQI feedback from the WTRU every normal CQI feedback period.